[Python-Dev] New test failure, test_socket, WinXP (original) (raw)

Brett C. bac at OCF.Berkeley.EDU
Tue Jul 6 07:00:53 CEST 2004

Tim Peters wrote:

Fails every time, in release and debug builds:

test testsocket failed -- Traceback (most recent call last): File "C:\Code\python\lib\test\testsocket.py", line 311, in testGetServBy eq(socket.getservbyport(port2), service) AssertionError: 'http' != 'www' [Brett C.] Does it pass if you change "www" to "http" on line 292? Yup! I'm not going to check that in, though -- I don't really know what this test is doing.

So I found out why it might be failing on your box and not on other people's: do you get an exception raised when you call socket.getservbyname('ssh', 'tcp')? I bet you do and I bet everyone else who has this test passing doesn't or has an exception for 'www' as well. I just removed 'ssh' as an option and that led to a failure because it then tested 'www'.

So what follows is just a long explanation of the test and how I figured out what was happening so people know what I did to come to this conclusion and to possibly help anyone out who is curious about this networking stuff. If you only want to know what I suggest to fix the test, just jump past the tags.

OK, so here is how the test works (Lib/test/test_socket.py:287):

Obviously socket.getservbyport() is returning "http" instead of "www". If you look at Modules/socketmodule.c:2910 where socket_getservbyport() starts, you will see the thing just calls getservbyport().

Now, if you read pg. 251 or 255 in 'UNIX Networking Programming: Vol 1, Second Edition", you will see, as Guido pointed out in another email, getservbyport() usually gets its info from /etc/services (\Windows\system32\drivers\etc\services for you Windows users, or you can go to http://www.iana.org/assignments/port-numbers to get the official list). Now for Guido, Tim, and myself, the line for port 80 is http 80/tcp www www-http, with that going / .

All of this is info is returned in a servent struct which contains the name, aliases, port, and protocol. In socketmodule.c the code returns what is in the equivalent name field in the servent struct.

What does this all mean? It means Tim's failure is legit; socket.getservbyport() is supposed to return "http" based on what his OS has listed for port 80. The rest of us never hit it either because 'ssh' came up as a legit protocol or 'www' failed. Either way 'www' doesn't get down to the socket.getservbyport() test.

Couple options on fixing. We can just change it to 'http' to make it proper for what it returns if we don't care about testing for aliases. If we do care about checking for aliases we should, if the test fails, take the returned result and feed it into socket.getservbyname() and compare the return value; if they match the test actually does pass.

Personally I am +1 on changing 'www' to 'http' in the test and moving on. I am +0 on leaving it but adding the extra test of feeding differing results into socket.getservbyname() to catch alias->name issues like this since it does do an extra test (but that assumes the OS will have an alias of 'www').

Oh, and cvs annotate says Barry was the last one to touch both the 'for' loop statement and the socket.getservbyport() test lines. =)

-Brett

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